1. Field of the Invention
The present invention relates to an information storage device, and an information storage and regeneration method employing the information storage device. Particularly, it relates to a novel information storage device employing as an information storage material bistable molecules which undergo an isomerization reaction by electric carrier injection and electric characteristics of which change accompanying the isomerization reaction, and an information storage and regeneration method employing the information storage device.
2. Discussion of Background
In recent years, along with progress in information-related technology, demand for large capacity storage devices for storing information is growing. For information storage devices to be used for computers, (1) high speed recording and regeneration and (2) mass storage property are required, and further as additive performances required, (3) non-volatile properties with which no special electric power is required for holding information and (4) portability of the stored data are required. Particularly, the above performance (1) is important for memory which is closest to and frequently accesses the CPU, i.e. SRAM, DRAM, etc. of e.g. cash memory or main memory located within the CPU. Further, for the program body or for storage of large scale data by the program body, a hard disk drive which is excellent in the above performance (1) to a certain extent and which is excellent in the performances (2) and (3) is employed. Further, for storage of an enormous quantity of data and for distribution of the application soft and animation soft, optical disks particularly excellent in the performances (2), (3) and (4) are employed. Further, in recent years, for music and for digital cameras and mobile telephones, use of non-volatile semiconductor memory (flash memory) is rapidly increasing, as an information storage device which is mechanical less, which is compact and which is excellent in the performances (3) and (4).
For the above DRAM or semiconductor memory such as flash memory, although the above performances (1) or (3) and (4) are important, a need for mass storage (high integration) is also great, and technical development therefor has been actively carried out. The typical technology for high integration of the semiconductor is miniaturization technology, and it is to minify the so-called design rule. For example, Intel Corporation (U.S.A) announced a transistor having a gate length of 15 nm at 2001 International Electron Devices Meeting (2001 IEDM (Dec. 3-5, 2001)), and it is considered that high definition of such miniaturization develops as heretofore in the foreseeable future.
On the other hand, it has been known that development in miniaturization alone is insufficient, considering the above mass storage as a semiconductor memory device. For example, the special feature in NIKKEI ELECTRONICS 2001. 2. 12 (No. 789) p. 152, describes as follows.
Each cell constituting the memory device comprises a switch part such as a transistor and an information storage part such as a capacitor (in a case of DRAM), as shown in FIG. 5. The switch part may be miniaturized along with development in miniaturization technology, however, the information storage part can not be miniaturized. For example, in the past history of high integration of DRAM, the capacitor part is made to have three dimensions to secure the required stored charge, however, high integration by making the capacitor part have three dimensions reaches the limit. Thus, a memory device of new principle employing no capacitor, such as FeRAM, MRAM or phase change RAM has been proposed. Information is stored in a polarized state of ferroelectric in the case of FeRAM, by the magnetization direction of the magnetic material in the case of MRAM, or by the difference between the crystal state and the amorphous state of the phase change material in the case of phase change RAM, respectively.
However, in the case of such a memory device, it is necessary to handle an aggregate state of a large number of atoms constituting the storage part at the time of storing information, and accordingly storage tends to be difficult from its principle, if the size of the storage part is reduced and the number of the constituting atoms is reduced. Accordingly, difficulty in further high integration with such a memory device is in prospect.